110 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Considered in relation to underlying rocks, the structure of the stone 
reefs is best understood from the results obtained by the holes bored in 
the Pernambuco reef in 1874 by Sir John Hawkshaw. The following is 
the record of the deepest hole! put down. 
RECORD or BORING on THE PERNAMBUCO REEF. 
METRES, 
AIM. аа иа га 998 
NIG ав ee) 
SS src re BIO 
СУВИ л ш, sro eram уф 
DIE IT a i 
DMME и A еол, 
Mottled clay A ео и LOG 
Yellow clay RU D AA a e O 
(мери у ee xx 
УШ экы ы о Т et 
Other holes put down in the reef show that the surface rock is underlain 
by sands, shells, and clays, but there is no regularity in the sequence of 
these materials. 
Conelusions. —The stone reefs are nearly, but not quite, straight. 
The bedding of the materials dips seaward at the same angle as ordinary 
beach sands. The hard rock of the reef is only three or four metres 
thick. The underlying materials are sands, shells, and clays without 
regular sequence. The process of formation, the character, and the 
structure of the reefs show that they are ancient beaches hardened by 
lime carbonate, while their straightness shows that they are forms of a 
mature beach-line fixed and made permanent by the process of consoli- 
dation pointed out in Part УТ., pp. 171-198. 
1 Melhoramento dos portos do Brazil, p. 15. Rio de Janeiro, 1875. 
